1. Field of the Invention
The present invention relates to a solid-state imaging device and, more particularly, to a technique which is effective when applied to a solid-state imaging device having a solid-state imaging element chip for receiving optical signals through an optical low-pass filter.
2. Description of the Prior Art
In the solid-state imaging device to be used in a video camera, the solid-state imaging element has its surface receive the optical signals, which are condensed by an optical lens, to transform the received signals into electric signals by the solid-state imaging element chip. The solid-state imaging device is equipped with the optical low-pass filter (LPF) between the optical lens and the solid-state imaging element chip so as to reduce the Moire effect which will deteriorate the image quality. The optical low-pass filter is made of a quartz plate which has an excellent controllability of the path for the optical signals and a high optical transmissivity.
Incidentally, the Moire effect of the solid-state imaging device is disclosed on pp. 134 and 135 of "SolidState Image Device" issued on July 30, 1986 by Kabushiki Kaisha Shokodo and edited by TV Association.
We have happened to discover that the fixed pattern noises dropped in their characteristic tests of a solidstate imaging device when we forgot the optical low-pass filter demounted. On the basis of this fact, we have moved the optical low-pass filter toward and apart from the solidstate imaging element chip to confirm that the fixed pattern noises change. In other words, we have confirmed that the fixed pattern noises depend highly upon the presence of the optical low-pass filter. According to our understanding, the clock signal (having a frequency of 11 MHz) of the solid-state imaging element chip impinge upon the optical low-pass filter to resonate with the intrinsic oscillations of quartz so that the resonated electromagnetic waves come incident as the reflected waves upon the solid-state imaging element chip to generate the fixed pattern noises. The clock signal is a transfer signal of the shift register of the solid-state imaging element chip. The fixed pattern noises raise a problem that the quality of the image to be projected by the solid-state imaging device is deteriorated.